EAS Publications Series
Volume 31, 2008Far-Infrared Workshop 2007
|Page(s)||43 - 46|
|Published online||04 October 2008|
C. Kramer, S. Aalto and R. Simon (eds)
EAS Publications Series, 31 (2008) 43-46
Tracking Water, O2 and Ice in Molecular Clouds: PDRs Models with Photodesorption and Grain Chemistry
Dept. of Physics and Astronomy, San Jose State University, USA
2 Space Science and Astrobiology Branch, NASA Ames Research Center, USA
3 Astronomy Department, U. of Michigan, USA
4 Smithsonian Astrophysical Observatory, USA
Corresponding author: email@example.com
We have expanded our model of photodissociation regions (PDRs) to include the freezing of O- and C-bearing species on dust grains, simple grain surface chemistry, and desorption processes, including photodesorption, that may be important in the surface layers of diffuse, translucent, and dense molecular clouds. The main result of including these processes is that a number of important gas-phase species, including H2O and O2, peak in abundance at AV ~ few into the cloud. Most of the gas-phase column, and most of the emission, from these species arises in the peak. Closer to the surface, H2O and O2 are photodissociated, while deeper into the cloud, they freeze out onto grain surfaces. The result is H2O and O2 column densities that are nearly constant for a wide range of gas densities, n, and for FUV fields G0 500. The roughly constant column densities of these species provides an explanation for the low line-of-sight average abundances of H2O observed toward GMCs. The model results also suggest that regions of high FUV field are the best places to search for O2.
© EAS, EDP Sciences, 2008
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